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Electronics > Theory 1.2 > Flashcards

Theory 1.2 Flashcards

1
Q

What is pulsating DC ?

A
  • Pulsating DC (PDC) is a type of direct current (DC) that varies in magnitude but never changes direction
  • DC fluctuates between zero and a peak value.
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2
Q

Adding any number of sine waves of the same frequency will always produce a sine wave of the same frequency with unique magnitude and phase.

TRUE OR FALSE

A

TRUE

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3
Q

Which waveform is leading/lagging ?

A
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4
Q

What is RMS ?

A
  • Equivalent ac voltage that would deliver the same power to a load as dc voltage
  • Same formula for current rms
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5
Q

What are the formulas for ac ohm’s law and power law. (For 100% ohmic element)

A
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6
Q

What happens when a charged capacitor is grounded at only one side ?

A
  • no discharge occurs, direct path must exist btw the 2 plates.
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7
Q

What is capacitance ?

A
  • The ratio of the electric charge on one plate to the potential difference (voltage) between the plates.
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8
Q

What is leakage current in capacitors?

A
  • Is the small amount of unintended current that flows across the dielectric material when a capacitor is charged.
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9
Q

How do electrolytic capacitors work ?

A
  • They use aluminium-foil plates with semi conducting chemical compound btw them.
  • Dielectric = thin film of insulating material, forms on 1 set of plate through electrochemical action when dc volt is applied
  • NOT used in ac applications
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10
Q

What happens to voltage and current during capacitor charging and discharging?

A
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11
Q

What is energy formula for capacitor ?

A
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12
Q

What is RC Time Constant ?

A
  • RC time constant is the time it takes for the voltage across the capacitor to either charge or discharge to approximately 63.2% or 37.8% of its final value.
  • Capacitor fully charges or discharges after 5 time constant ( 5 tau)
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13
Q

what is stray capacitance ?

A
  • its unintentional capacitance that exists between parts of a circuit that are not supposed to act as capacitors.
  • This happens due to the close proximity of conductors, like wires or circuit traces, which can cause a bit of a charge buildup between them.
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14
Q

What are the formulas for capacitors in parallel and in series ?

A
  • Capacitors in parallel add up.
  • Voltage limited to the capacitor with smallest volt rating
  • For cap in series, total cap < smallest cap
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15
Q

What does the graph of AC current applied to capacitor look like.

A
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16
Q

Is power dissipated in capacitive reactance as heat or any form of energy ?

A
  • Capacitive reactance doesn’t dissipate power, energy is alternately stored and released with each AC cycle
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17
Q

What is Self Resonant Frequency in capacitors ?

A
  • It’s the frequency where the capacitor’s own inductive and capacitive properties cancel each other out.
  • Beyond this point, the capacitor’s impedance starts to increase, and it behaves like an inductor.
  • Defines the maximum effective frequency range of the capacitor.
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18
Q

What is the formula for capacitive divider ?

A
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19
Q

What is the relationship btw electromagnetic fields and stationary, moving(constant velocity) and accelerating charges ?

A
  • Stationary Charge = electric fields surround the charge
  • Moving Charge = magnetic field surround moving charge
  • Accelerating Charge = kink created in electromagnetic field, electromagnetic waves radiates out.
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20
Q

What happens to the magnetic fields of electrons in a conductor without applied voltage?

A

Without applied voltage, the magnetic fields of electrons point in random directions, resulting in a net magnetic field of zero.

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21
Q

What occurs when a voltage is applied across a conductor in context of magnetic field?

A

When a voltage is applied, free electrons gain a drift component, generating a net magnetic field.

22
Q

What is the direction of the magnetic field in relation to conventional current flow?

A

The magnetic field is perpendicular to the direction of conventional current flow and follows the right-hand rule.

23
Q

What is the right-hand rule?

A

In the right-hand rule, your thumb points in the direction of conventional current flow, and your fingers curl in the direction of the magnetic field.

24
Q

What generates the magnetic field in a permanent magnet?

A
  • By the motion of unpaired electrons orbiting the nucleus of an atom.
25
Q

What role does the lattice structure of ferromagnetic materials play?

A

The lattice structure fixes a large portion of atomic magnetic dipoles in a fixed direction, creating a net magnetic dipole.

26
Q

How does placing a ferromagnetic material inside a solenoid affect the magnetic field?

A

Placing a ferromagnetic material inside a solenoid increases the magnetic field strength by aligning the core’s atomic magnetic dipoles.

27
Q

How do you determine the direction of force on a positive charge in a magnetic field?

A
  • Use your right hand
  • Left hand for negative charge
28
Q

What happens when a charge moves parallel to the applied magnetic field?

A

It experiences no force due to the magnetic field.

29
Q

What is the interaction between two wires carrying current?

A

The net magnetic field of one wire will exert a force on the other wire and vice versa, provided the current is fairly large.

30
Q

According to Faraday’s law, what induces EMF in a circuit?

A

EMF is directly proportional to the time rate of change of the magnetic flux through the circuit.

31
Q

What are the ways EMF can be induced in a circuit?

A
  1. The magnitude of B can vary with time
  2. The area of the circuit can change with time
  3. The angle between B and the normal of A can change with time
  4. Any combination of these can occur.
32
Q

What is the difference between an AC generator and a DC generator?

A

A DC generator uses a split ring or commutator for contacts, resulting in a pulsating direct current.

33
Q

What is self-inductance?

A

Self-inductance is the phenomenon where a looped wire generates an induced EMF due to the varying current passing through it.

34
Q

What does Faraday’s law of induction state regarding self-induction?

A

According to Faraday’s law of induction, self-induction occurs when the magnetic field through a loop grows or shrinks due to changes in current.

35
Q

What is the role of self-induction in inductors?

A
  • Used to store and release energy as current levels fluctuate in time-dependent circuits.
36
Q

What happens when a switch in a circuit is closed? (In relation to self-induced EMF)

A

When the switch is closed, the current does not jump immediately to V/R; instead, it increases rapidly, inducing an EMF that opposes the current flow.

37
Q

What is a self-induced EMF?

A

A self-induced EMF is the induced EMF that opposes the current flow in a circuit when the current changes.

38
Q

How do inductors differ from simple circuits regarding self-induction?

A

Inductors are designed to generate large concentrations of magnetic flux and experience significant self-induction during changes in current.

39
Q

What is the common geometry of inductors?

A

Inductors commonly have a looplike geometry, such as solenoids, toroids, or spiral shapes.

40
Q

What is the advantage of using a magnetic core in inductors?

A

Using a magnetic core allows for generating higher magnetic field densities and achieving desired inductance with fewer turns of wire.

41
Q

What are adjustable inductors?

A

Adjustable inductors are inductors whose effective coil length can be altered, typically using a slider or a slug made of different materials.

42
Q

What is a ferrite bead?

A

A ferrite bead is a device that increases the inductance of a wire by placing it through a hollow bead, absorbing RF radiation and converting it into heat.

43
Q

What is the typical application of ferrite beads?

A

Ferrite beads are often used on cables to prevent RF radiation (EMI) from interfering with electronic equipment.

44
Q

What is the primary function of an inductor?

A

An inductor acts like a time-varying current-sensitive resistance, resisting changes in current.

45
Q

How does an inductor behave under steady-state DC conditions?

A

Under steady-state DC conditions, an inductor passes current as if it were a wire.

46
Q

What happens when voltage increases across an inductor?

A

The inductor acts like a time-dependent resistor, resisting rapid increases in current.

47
Q

What occurs when voltage decreases across an inductor?

A

The inductor acts like a time-dependent voltage source, attempting to keep current flowing.

48
Q

What is reverse and forward EMF in the context of an inductor?

A
  • Reverse EMF is the induced EMF that points in the opposite direction of the applied voltage during an increase in current.
  • Forward EMF is the induced EMF that points in the same direction as the applied voltage during a decrease in current.
49
Q

What happens when an inductor is energized and de-energized suddenly?

A
  • Electrical energy is transformed into a magnetic field, and inductive behavior affects circuit dynamics.
  • The magnetic field energy is transformed back into electrical energy, affecting current flow.
50
Q

What is the effect of closing a switch in an inductor, capacitor and resistor circuit?

A
  • The lamp will light up brightly but quickly dims out due to the inductor’s high initial impedance.
  • The lamp slowly builds up in brightness until it reaches maximum illumination.
  • Free-electron flow is essentially instantaneous, and the brightness of the lamp remains constant.

Electronics (3 decks)

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